Since 1,3,3,3-tetrafluoropropene contains a double bond in the molecule, it decomposes rapidly in the atmosphere and is an environment-adaptive fluorocarbon having no concern for the effect on the ozone layer depletion, the global warming, etc. Furthermore, 1,3,3,3-tetrafluoropropene is a fluorine-containing olefin, and there exist cis-trans isomers. In the following, using the identification number and the additional sign, trans-form may be referred to as 1234zeE, and cis-form as 1234zeZ. In the case of no distinction between trans-form and cis-form, or of a mixture of them, it may be referred to as 1234ze.
As methods for producing 1,3,3,3-tetrafluoropropene (1234ze), the methods described in Patent Publication 1 to Patent Publication 3 can be mentioned.
Patent Publication 1 discloses a method for producing 1,3,3,3-tetrafluoropropene (1234ze) by reacting 1,1,1,3,3-pentafluoropropane (in the following, may be referred to as 245fa) with a potassium hydroxide aqueous solution in the presence of a crown ether.
In a method for producing 1,3,3,3-tetrafluoropropene (1234ze) by subjecting 1,1,1,3,3-pentafluoropropane (245fa) to a dehydrofluorination reaction in a gas phase in the presence of a catalyst, Patent Publication 2 discloses a method for producing 1,3,3,3-tetrafluoropropene (1234ze) by using a zirconium compound-supported catalyst prepared by supporting a zirconium compound on a metal oxide or an activated carbon.
Patent Publication 3 discloses a method for producing 1234ze, comprising the step of reacting 1,1,1,3,3-pentachloropropane (in the following, may be referred to as 240) with hydrogen fluoride to obtain 1-chloro-3,3,3-trifluoropropene (in the following, may be referred to as 1233zd) and the step of reacting the obtained 1233zd with hydrogen fluoride in a gas phase in the presence of a fluorination catalyst to obtain 1,3,3,3-tetrafluoropropene (1234ze). In the above-mentioned 1-chloro-3,3,3-trifluoropropene (1233zd), there exist cis-trans isomers. In the following, trans-form may be referred to as 1233zdE, and cis-form as 1233zdZ. In the case of no distinction between trans-form and cis-form, or of a mixture of them, it may be referred to as 1233zd.
Furthermore, in the field of refrigerants, working fluids, foaming agents, intermediates for medicines and agrochemicals, or electronic materials, in the case of using trans-1,3,3,3-tetrafluoropropene (1234zeE), it is preferable that 1234zeE has a high purity without containing impurities. In uses for refrigerants, working fluids, and foaming agents, particularly in the case of using as a refrigerant for car air conditioners, 1234zeE of high purity is preferred.
In particular, it is not preferable to have contamination of 1234zeE by CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons) or HFCs (hydrofluorocarbons), as impurities, which are saturated compounds. In these compounds, there are ones that are stable in the atmosphere and cause the ozone layer depletion or global warming and ones that show toxicity. Therefore, in case that 1234zeE contains these compounds as impurities, it has been a problem of necessity to remove them.
The impurities to contaminate 1234zeE can be exemplified by 142 (C2H3ClF2 (presumed structure: CF2HCH2Cl)), 244fa (CF3CH2CHClF), and 245fa (CF3CH2CHF2), which are saturated compounds. They can be exemplified by 1234zc (CHF2CH═CF2), 1243zf (CF3CH═CH2), CF3C≡CH, 1233zd (CF3CH═CHCl) or cis-1,3,3,3-tetrafluoropropene (1234zeZ, cis CF3CH═CHF), which are unsaturated compounds. In the following, these compounds may be referred to by their identification numbers.
A solid adsorbent, such as zeolite or alumina, is capable of increasing purity of fluorinated hydrocarbons or fluorinated unsaturated hydrocarbons by an adsorptive reduction of hydrogen fluoride, alcohols, etc. contained in the fluorinated saturated hydrocarbons or the fluorinated unsaturated hydrocarbons. Patent Publication 4 discloses a method of an adsorptive reduction of hydrogen fluoride, which is contained in fluorinated hydrocarbons and fluorinated unsaturated hydrocarbons, by such solid adsorbent. Patent Publication 5 discloses a method of an adsorptive reduction of alcohols. Patent Publication 6 discloses a method for drying a fluid comprising a fluoropropene, which method comprises the step of contacting the fluid with a desiccant comprising a molecular sieve having openings which have a size across their largest dimension of from 3 angstroms to 5 angstroms.
As in the methods described in Patent Publications 4-6, it is publicly known to selectively adsorb only small molecules, such as hydrogen fluoride or alcohols, into micropores of zeolite. There is, however, not known a method of conducting a selective adsorptive removal of impurities that have molecular structures and sizes similar to those of the target product.